1. Field of the Invention
This invention relates to flash spinning of plexifilamentary film-fibril strands of polyester. This invention also relates to a spin fluid that may be used in existing commercial equipment with minimum changes in the equipment and to a spinning process using existing commercial equipment in which the spinning process utilizes compounds having very low ozone depletion potential, and the compounds are either non-flammable or exhibit very low flammability.
2. Description of the Related Art
U.S. Pat. No. 3,081,519 to Blades and White describes a flash spinning process for producing plexifilamentary film-fibril strands from fiber-forming polymers. A solution of the polymer in a liquid, which is a non-solvent for the polymer at or below its normal boiling point, is extruded at a temperature above the normal boiling point of the liquid and at autogenous or higher pressure into a medium of lower temperature and substantially lower pressure. This flash spinning causes the liquid to vaporize and thereby cool the extrudate which forms a plexifilamentary film-fibril strand of the polymer. Preferred polymers typically include crystalline polyhydrocarbons, such as polyethylene and polypropylene.
According to Blades and White, a suitable liquid for flash spinning (a) has boiling point that is at least 25xc2x0 C. below the melting point of the polymer; (b) is substantially unreactive with the polymer at the extrusion temperature; (c) should be a solvent for the polymer under the pressure and temperature set forth in the patent (i.e., these extrusion temperatures and pressures are respectively in the ranges of 165 to 225xc2x0 C. and about 500 to 1500 psia (3447-10342 kPa)); (d) should dissolve less than 1% of the polymer at or below its normal boiling point; and (e) should form a solution that will undergo rapid phase separation upon extrusion to form a polymer phase that contains insufficient solvent to plasticize the polymer.
Commercial flashspun products have been made primarily from polyethylene plexifilamentary film-fibril strands and have typically been produced using trichlorofluoromethane as a spin agent. However, it would be desirable to make flashspun products from other types of polymers, such as polyesters, for example that have different properties than polyethylene.
Flash spinning of some types of polyester is known. U.S. Pat. No. 3,401,140 to Blades et al. discloses 10-80 weight percent of poly(ethylene terephthalate) in methylene chloride or in a mixture of methylene chloride and a perhaloalkane. U.S. Pat. No. 3,227,784 to Blades discloses poly(ethylene terephthalate) in mixtures of methylene chloride with cyclohexane, dichloro-difluoromethane, or dichloro-tetrafluoroethane.
Japanese Patent Publication J06257012, Sep. 13, 1994, discloses that a highly fibrillated network of fibers can be made of poly(ethylene terephthalate). The poly(ethylene terephthalate) may be present at 5-30% weight percent and flashspun from methylene chloride. The reference also states that poly(1,4-butylene terephthalate) can be used to make such fiber networks, but does not provide any details beyond the bare disclosure.
International Patent Publication WO 97/25459 (Jul. 17, 1997) assigned to E. I. du Pont de Nemours and Company (DuPont) is directed to plexifilamentary strands of various polyester blends, for example, poly(1,4-butylene terephthalate) (4GT) with poly(ethylene terephthalate) (2GT) and 4GT with poly(1,3-propylene terephthalate)(3GT). Poly(1,3-propylene terephthalate) may also be referred to as poly(trimethylene terephthalate). The reference also discloses plexifilamentary strands of polyester blended with various other polymers as well as 100% 4GT. The flash spinning was done using either a mixture of CO2 and water or solvents such as methylene chloride mixed with decafluoropentane (HFC-4310mee).
Microcellular and ultramicrocellular foams of 2GT are disclosed in U.S. Pat. No. 3,227,664 to Blades; U.S. Pat. No. 3,375,211 to Parrish; and U.S. Pat. No. 5,254,400 to Bonner et al., all assigned to DuPont. The solvents used were methylene chloride or mixtures of methylene chloride and dichloro-difluoromethane.
The invention includes a process for the preparation of plexifilamentary film-fibril strands of synthetic fiber-forming polymer which comprises flash spinning synthetic fiber-forming polyesters of poly(1,3-propylene terephthalate), copolymers of poly(1,3-propylene terephthalate), poly(1,4-butylene terephthalate) and copolymers of poly(1,4-butylene terephthalate). Spin agents that can be used include 1,1,2-trichloro-2,2-difluoroethane and isomers thereof; 1,2-dichloroethylene; and dichloromethane.
The invention includes a spin fluid comprising polyesters of poly(1,3-propylene terephthalate), copolymers of poly(1,3-propylene terephthalate), poly(1,4-butylene terephthalate) and copolymers of poly(1,4-butylene terephthalate) and selected spin agents as listed above.
The invention also includes processes for making microcellular and ultramicrocellular foams made from poly(ethylene terephthalate), poly(1,3-propylene terephthalate), or poly(1,4-butylene terephthalate).
The invention further includes processes for making blends of polyethylene with poly(ethylene terephthalate), poly(1,3-propylene terephthalate) or poly(1,4-butylene terephthalate).